Method for making ceramic titanate elements and materials therefor

ABSTRACT

A method for making ceramic titanate elements and materials therefor, particularly semiconducting lanthanide-doped barium titanate elements having positive temperature coefficients of resistance for use as solid-state sensors or the like, is shown to comprise the steps of dissolving the titanium chelate of triethanolamine with selected alkaline earth salts such as barium acetate and with selected lanthanide salts such as lanthanum acetate in a solvent to form a common solution. Alternatively, tetraisopropyl titanate mixed with lactic acid is combined with selected alkaline earth salts such as barium acetate and with selected lanthanide salts such as lanthanum acetate in a solvent to form a common solution. The solution is then heated, initially to form a semisolid material and thereafter-in an oxidizing or neutral atmosphere-to calcine the semisolid material to form the desired titanate material. The resulting titanate material is then combined with a binder, is pressed into a desired shape, and is fired at high temperature to form the desired ceramic titanate elements.

mam @tates Patent Faxon et al. [4 1 Jan. 25, W72

54 METHOD FtOR MAKING CERAMHQ 3,340,074 9/1967 nerikjgf.T111111?..252/520 TITANATE ELEMENTS ANB 3,351,568 1 1/1967 Waseleski et al.106/39 MATERIALS THEREFOR Robert C. Faxon, Attleboro, Mass; Robert T.McGovern, Providence, R].

[72] Inventors:

Texas Instruments Hncorporated, Dallas, Tex.

[22] Filed: May 1,1970

[21] Appl.No.: 33,962

[73] Assignee:

Related [1.8. Application Data [63] Continuation-impart of Ser. No.651,992, July 10,

1967', abandoned.

Primary Examiner- Douglas J. Drummond AttorneyHarold Levine, Edward J.Connors, Jr., John A. Haug, Gerald B. Epstein and James P. McAndrews[57] ABSTRACT A method for making ceramic titanate elements andmaterials therefor, particularly semiconducting lanthanide-doped bariumtitanate elements having positive temperature coefficients of resistancefor use as solid-state sensors or the like, is shown to comprise thesteps of dissolving the titanium chelate of triethanolamine withselected alkaline earth salts such as barium acetate and with selectedlanthanide salts such as lanthanum acetate in a solvent to form a commonsolution. Alternatively, tetraisopropyl titanate mixed with lactic acidis combined with selected alkaline earth salts such as barium acetateand with selected lanthanide salts such as lanthanum acetate in asolvent to form a common solution. The solution is then heated,initially to form a semisolid material and thereafter-in an oxidizing orneutral atmosphereto calcine the semisolid material to form the desiredtitanate material. The resulting titanate material is then combined witha binder, is pressed into a desired shape, and is fired at hightemperature to form the desired ceramic titanate elements.

26 Claims, No Drawings METHOD FOR MAKING CERAMIC THTANATE ELEMENTS ANDMATERIALS THEREFOR This application is a continuation-in-part of apreviously filed, copending application Ser. No. 65 l ,992 for patententitled Method for Making Ceramic Titanate Materials and Tilements"filed by the coinventors hereof on July I0, 1967, which previously filedapplication was assigned to the assignee of the present application, andis now abandoned.

In known prior art methods for making semiconducting ceramic elements oftitanate materials such as barium lanthanum titanate, considerabledifficulty has been experienced in consistently reproducing materials ofthe desired physical and electrical properties. For example, in oneprior art process, barium carbonate and lanthanum carbonate particleshave been mechanically mixed together with titanium dioxide particlesand have been calcined to produce a titanate material. This material isthen pressed and fired to form the desired ceramic elements. In thisprocess, impurities are introduced with the raw materials, particularlythe titanium dioxide; the raw materials tend to be inadequately mixed,and additional contaminants are frequently introduced during themechanical mixing; some undesirable crystalline transformations such asanatase-to-rutile transformation of titanium dioxide occurs during theprocess; and the ceramic-forming materials produced by the processfrequently do not have the desired physical and electrical properties.Similarly, in a prior art wet chemical process, wherein raw materialsare reacted in solution to form a titanate or intermediate titaniummaterial within the solution, the desired reactions are difficult tocontrol, the raw materials are expensive, and the process does notalways produce, ceramic-forming materials of the desired physical andelectrical properties.

It is object of this invention to provide a novel and improved processfor making titanate materials of perovskite structure; to provide such aprocess for making semiconducting, bariumtitanate-based elements with apositive temperature coefficient of resistance for use as solid-statesensors and the like; to provide such a process which produces ceramictitanate elements of predictable and consistently reproducible physicaland electrical characteristics; to provide such a process which utilizesinexpensive and commercially available raw materials; to provide such aprocess which is simple and inexpensively performed; to provide such aprocess which produces ceramic-forming titanate materials of desiredphysical and electrical characteristics at substantially lower coststhan have previously been possible; and to provide such a process whichis especially suited for commercial production purposes.

Briefly described, the novel and improved method of this inventionincludes the steps of combining reactant materials in at least onesolvent to form a common solution. In this way, the reactant materialsare provided with thorough mixing with respect to each other. Thesolution is then heated to produce a semisolid substance in whichsegregation of the homogeneously mixed reactants is significantlyretarded. Heating of the substance is then continued in an oxidizing orneutral atmosphere for calcining the substance to form a desiredtitanate material.

In one embodiment of the process of this invention, for example, thetitanium chelate of triethanolamine is combined with selected alkalineearth salts such as barium acetate or a mixture of barium acetate andstrontium acetate in a common solution. The solution is then heated toform a gel and the gel is heated for calcining the noted materials toform the desired titanate material. This titanate material is then mixedwith a binder, is pressed into the desired shape, and is fired at hightemperature to form a ceramic titanate element of the desired physicaland electrical characteristics.

In an alternate embodiment of the process of this invention,tetraisopropyl titanate is mixed with lactic acid and is combined withselected alkaline earth salts such as barium acetate in a commonsolution. The solution is then heated to form a foamlike substance andthis substance is heated for calcining the noted materials to form thedesired titanate material. This titanate is them processed to formceramic titanate elements as above described.

In forming semiconducting ceramic titanate elements with positivetemperature coefficients of resistance for use as solidstate sensors orthe like in accordance with this invention, lanthanide salts such aslanthanum acetate or cerium acetate are incorporated in the materialsabove described. These lanthanide salts are added either to the commonsolution used in forming the gel or foamlike materials above describedor are added to the calcined titanate materials together with the notedbinder. In this way subsequent firing of the noted titanate materials inthe manner above described produces the desired semiconducting ceramictitanate elements.

The use of an organic titanium compound, which is commercially availablein highly purified form, avoids the introduction of impurities in theinitial raw materials used in the process. The combination of theorganic titanium compound and the alkaline earth and lanthanide salts ina common solution which is subsequently converted to semisolid form andcalcined assures the formation of homogenous titanate materials. Inaddition because the titanium-bearing reactant employed in the processis not in the form of the titanium dioxide, crystalline transformationof the raw materials is avoided and production of materials of thedesired perovskite structure is assured. Further the process is simplyand inexpensively performed and consistently provides ceramic titanateelements of the desired electrical and physical properties.

Other objects, advantages, and details of the methods of this inventionappear in the following detailed description of preferred embodiments ofthe invention.

In accordance with the method of this invention, ceramicforming titanatematerials and ceramic elements are produced from raw materials which areinitially combined in a common solution. That is a first solution isprepared by dissolving the titanium chelate of triethanolamine in aselected solvent, preferably in a concentration comprising about percentby weight of the organic compound. The preferred triethanolamine chelatedipropoxytitanium bis- (triethanolamine) having the formula Ti(C;,l-I,O)([C H ,O] NC H O) is represented by the following structure:

.. -..-k ta stiit srgatqmi Preferably, the titanium chelate oftriethanolamine is dissolved in isopropyl alcohol. This material iscommercially available in the described solution from E. I. duPont deNemours and Company, Inc. of Wilmington, Del. under the trade nameTYZORTE, a product which represents a highly purified form of theorganic substance.

A second solution is then prepared by dissolving an alkaline earth saltsuch as barium acetate in a solvent such as distilled water. Preferablya reagent grade of the salt is employed and a minimum amount of water isused for dissolving the selected alkaline earth salt.

These first and second solutions are then combined to form a commonsolution, sufficient quantities of the first and second solutions beingemployed so that the common solution embodies substantially equal molarquantities of the organic titanium compound and of the barium acetatematerial. In this regard, it is preferred that the molar quantity of theorganic titanium compound slightly exceed the molar quantity of thebarium salt in the common solution by as much as about 3 percent, andpreferably by about 0.3 percent, for reasons to be hereinafterdescribed. As the proportions of the organic titanium compound andalkaline earth salt used in the common solution are important, the rawmaterials used are preferably analyzed in any conventional manner priorto use to determine their exact content of active constituents.

After thorough mixing of the common solution 'to assure uniformdistribution of the active constituents thereof, the common solution ispreferably permitted to form a semisolid material or gel. Gelling willoccur upon permitting the solution to stand for a sufficient period oftime at room temperature, but preferably the common solution is gentlyheated at a term perature up to approximately 80 C. to induce gelation.

This semisolid material or gel is then heated in an oxidizing or neutralatmosphere for calcining the constituents of the gel or form the desiredtitanate material. This calcination can be performed in air in anyconventional calcining furnace and the gel is preferably placed on azirconia plate or platinum foil during calcination. It is found that thegel can be calcined at a temperature as low as 600 C., and temperaturesas high as l,l50 C. have been used, but preferably the mixture iscalcined at a temperature of about 950 C. for a period of at least lhour. During such calcining, the organic constituents of the originalraw materials are oxidized and driven out of the mix ture whereas theactive constituents of the raw materials react to form the desiredbarium titanate material. In the heating process, the gel at first turnsblack and shrinks considerably. It then ignites and burns with aluminous flame, and finally forms white porous lumps of barium titanate.After cooling, these lumps are crushed or pulverized in any conventionalmanner to form a white powder which is then sieved to form a finelydivided, particulate material.

Alternatively, a separate heating step for forming a gel is omitted.That is, the noted common solution is directly heated for calciningconstituents of the solutions. In this arrangement, the initial heatingof the solution tends to rapidly produce the semisolid substance or geland subsequent heating results in driving off organic constituents ofthe gel and in reacting of the active constituents of the gel to formthe desired barium titanate material.

In order to facilitate use of this calcined particulate material informing ceramic titanate elements, a binder solution is preferablyprepared and added to the particulate. For example, a saturated solutionof polyvinyl alcohol in distilled water, embodying about 50 grams ofpolyvinyl alcohol per liter of water, is added to the calcinedparticulate and is thoroughly mixed with the particulate to form asmooth slurry. This slurry is then dried by mild heating to form abinder mixture. Preferably sufficient binder solution is used so thatthe resulting binder mixture embodies about 1 percent by weightpolyvinyl alcohol.

The dried binder mixture is preferably but not necessarily subjected toisostatic or hydrostatic compaction at this stage in order to increasethe density of the binder mixture to facilitate subsequent pressing ofthe mixture in forming ceramic elements. After isostatic compaction, theresulting compacted mixture is again crushed or pulverized and sieved.

The resulting barium titanate powder is then subjected to a finalcompaction in an appropriately shaped mold so that the mixture ispressed together to form an intermediate element of the desired shape.The binder mixture is preferably compacted under pressure on the orderof 5,000 pounds per square inch to assure proper density of the elementwithout introducing cracks or other defects in the element. The pressedintermediate element is then sintered or fused in air, preferably on azirconia plate or platinum foil, for fusing the ban'um titanateparticles together and for volatilizing and driving off the polyvinylalcohol binder material. The intermediate element is fired at atemperature of at least about l,300 C. and preferably at a temperatureof about 1,45 C. to form the desired ceramic barium titanate elements.The slight excess of the titanium chelate or triethanolamine used informing the described gel facilitates sintering or fusing of the bariumtitanate elements.

The barium titanate element formed by the process has the desiredperovskite structure and displays high resistivity. Measurement of thecapacitance of the barium titanate indicates that the element displaysthe anomalous characteristics in response to temperature change that areusually associated with ceramic titanate materials of perovskitestructure. The

element material displays a curie point of approximately 128 C.

1n accordance with another embodiment of the method of this invention,semiconducting ceramic titanate elements with positive temperaturecoefficients of resistance for use as solidstate sensors or the like arealso produced from raw materials which are initially combined in acommon solution and are subsequently gelled and calcined. That is, afirst solution embodying the titanium chelate of triethanolamine isprepared in the manner above described. A third solution is thenprepared by dissolving an alkaline earth salt such as barium acetate ina solvent such as distilled water together with a selected lanthanidesalt such as lanthanum acetate or cerium acetate. For example, where thethird solution is to be used in producing barium lanthanum titanatematerial having the empirical formula Ba,,,,,,La., ,,,,Ti,,,,,o,, 510.9grams of barium acetate and 1.03 grams of lanthanum acetate aredissolved in a minimum amount of water to form the third solution.

These first and third solutions are then combined to form a commonsolution, sufficient quantities of the first and third solutions beingemployed so that the common solution embodies substantially equal molarquantities of the titanium chelate of triethanolamine and of thecombination of the barium and lanthanum acetate. In this regard, it ispreferred that the common solution embody a slight molar excess oftriethanolamine for the purposes previously described.

After thorough mixing of this common solution, the solution is heated toform a gel and to calcine the gel in the manner previously described andforms the desired barium lanthanum titanate material in the forms of adry particulate, the particulate then being combined with the bindermaterial, pressed and fired in the manner above described for formingceramic barium lanthanum titanate elements. These elements display verydesirable semiconducting properties, display low resistivity at roomtemperature, have a curie point of about 125 C., and display a very highslope or increase in resistivity per degree centigrade rise intemperature close to 125C.

In another embodiment of the method of this invention for makingsemiconducting ceramic titanate elements, first and second solutions areprepared in the manner described above with reference to the formationof barium titanate materials. These first and second solutions are thencombined in appropriate quantities to form a common solution embodyingsubstantially equal molar quantities of the titanium chelate oftriethanolamine and of barium acetate. The common solution is thenheated to form a gel and to calcine the gel in the manner previouslydescribed to form a dry barium titanate particulate.

An aqueous solution of a lanthanide salt such as lanthanum acetate isthen prepared, preferably in a concentrated solution, and is combinedwith a quantity of the previously described aqueous polyvinyl alcoholbinder solution. This combined lanthanide and binder solution is thenadded to the calcined barium titanate particulate described immediatelyabove to form a smooth slurry, a sufficient quantity of the lanthanideand binder solution being used so that the slurry embodies about 0.15mole percent of the lanthanide dopant. The slurry is then dried, pressedand fired in the manner previously described to form the desired ceramicbarium lanthanum titanate elements having the empirical formula Ba La TiO These elements display the desirable semiconducting properties of thebarium lanthanum titanate elements made by the method previouslydescribed.

In another embodiment of the method of this invention, ceramic titanateelements having a lower curie point are made by substituting anappropriate quantity of a strontium salt such as strontium acetate for acorresponding molar quantity of barium salt in any of the methodspreviously described. For example, in making a semiconducting titanatematerial having an C. curie point, a first aqueous solution of thetitanium chelate of triethanolamine is prepared in the manner abovedescribed. A fourth solution is then prepared by dissolving bariumacetate and strontium acetate together with lanthanum acetate indistilled water, sufficient quantities of the salts being used so thatthe fourth solution embodies 84.85 mole percent barium acetate, molepercent strontium acetate, and 0.15 mole percent lanthanum acetate.These first and fourth solutions are then combined to form a commonsolution embodying substantially equal molar quantities of the titaniumchelate of triethanolamine and of the combination of the barium,strontium and lanthanum salts; the solution is gently heated to form agel; and the gel is calcined in a manner previously described to form abarium strontium lanthanum titanate particulate material having theempirical formula Ba,, ,,,,sr, ,,,,,,La,, ,,,,Ti, ,,,o,. Thisparticulate is then combined with a binder, is pressed and is fired inthe manner described to form the desired semiconducting ceramic elementhaving a curie point of about 80 C.

ln another preferred embodiment of this invention, a master solution isprepared by dissolving tetraisopropyl titanate in a lactic acid solutionsuch as in an aqueous lactic acid solution. For example, in a preferredarrangement, 1.25 kilograms of lactic acid (85 percent concentration byweight) is thoroughly mixed with 0.87 kilogram of deionized water. Aquantity of I kilograms of tetraisopropyl titanate (embodying l6.8percent titanium by weight) is then added to the lactic acidwatermixture, preferably in the form of small high-pressure streams of thetetraisopropyl titanate accompanied by vigorous mixing of the materialsas they are combined. Pouring of the tetraisopropyl titanate into thelactic acid-water mixture, or too rapid addition thereof to the mixture,will tend to result in the formation of lumps and will tend to produce arapid rise in solution temperature. Addition of tetraisopropyl titanateshould be conducted slowly and should be regulated to maintain thesolution temperature below about 65 C. to avoid excessively rapidformation of alcohol vapors over the solution, and to avoid ignition ofsuch alcohol vapors.

While lactic acid is preferred for dissolving the tetraisopropyltitanate material other organic acids such as acetic acid andwater-soluble alphahydroxy acids can also be used.

Preferably after a 24-hour dissolution period during which the solutionis stirred substantially, the pH of the solution is adjusted to about7.5 to 8.5 and preferably to about 8.0. Where this master solution is tobe used immediately, this adjustment of solution pH is not absolutelyrequired. However, for best results where the solution is to be made upwell in advance of actual use of the solution, the noted pH adjustmentserves to stabilize the solution. Adjustment of the pH is preferablyaccompanied by addition of ammonium hydroxide (28 percent concentrationby weight for example). If dissolution of the tetraisopropyl titanatematerial in the solution is not complete after permitting the mastersolution to stand for an additional 24 hours, it will be desirable tofilter the solution to remove floating particles of titanium dioxide andthe like.

After preparation of this master solution, the solution is preferablyanalyzed by pyrolysis to precisely determine the effective titaniumdioxide content of the solution. For example, a sample of the solutionis preferably subjected to heating at a temperature of about 85 C. forabout 8 hours to initiate solvent evaporation and is then heated to atemperature of about 900 to 1,000 C. to complete the pyrolysis. Afteranalysis of the solution, the master solution is preferably stored in atightly closed container to maintain solution concentrations.

In accordance with this invention, a selected quantity of this mastersolution required for producing a specific size of batch ofceramic-forming titanate material is segregated. A sufficient quantityof water and of a selected alkaline earth salt such as barium acetateare added to the segregated portion of the master solution to form acommon solution which is hereinafter designated as a fourth solution.The quantity of barium acetate, or other alkaline earth salt, added tothe segregated portion of the master solution is elected so that saidfourth solution embodies substantially equal molar quantities of theorganic titanium compound and of the barium acetate material, Thequantity of water added to said segregated master solution is preferablyselected to provide the fourth solution with an efiective bariumtitanate content corresponding to about l5 percent barium titanate byweight. In this regard, the molar quantity of the organic titaniumcompound in the fourth solution preferably exceeds the molar quantity ofbarium acetate to a slight degree (by about 0.3 to 3.0 percent forreasons previously described). However, the fourth solution can also beprepared as a slightly barium-rich solution within the scope of thisinvention. After preparation of said fourth solution, the pH is thenpreferably adjusted, by addition of acetic acid or ammonium hydroxidefor example, to render the fourth solution at least slightly acidic andpreferably to provide the fourth solution with a pH of about 6.0.

After preparation and pH adjustment of said fourth solution, thesolution is heated initially to form a semisolid substance or foam andsubsequently to calcine the substance to form a desired titanatematerial. For example, is a preferred step according to this invention,said fourth solution is placed in a ceramic or quartz boat and is heatedat a temperature in the range from about 650 to l,l50 C. in an oxidizingor neutral atmosphere until no carbon residue remains, thereby torapidly produce the semisolid substance or foam and to calcine thebarium and titanium ingredients of the solution. Preferably for example,the solution is heated to about 800 C. for about 1 hour or less foroxidizing and driving off the water and organic constituents of thesolution while reacting the active constituents of the solution toproduce the desired barium titanate material. In this heating process,the solution initially forms a semisolid substance of foamlike characterwhich results in considerable expansion of the material in the boats.For this reason fairly large boats which are initially only partlyfilled with said fourth solution are used in this heating step. Asheating of the semisolid, foam substance proceeds, the foam turns blackand shrinks somewhat in volume and then ignites to burn with a luminousflame. Finally, at completion of the calcining step, the foam formswhite porous lumps of barium titanate which are crushed or pulverized inany conventional manner to form a white powder, this powder then beingsieved to form a finely divided particulate material. The powderresulting from performance of this latter embodiment of the process ofthis invention is characterized by a very high degree of uniformitythroughout of body of the powder. Further, the powder particle size isdesirable small resulting in improved voltage sensitivitycharacteristics in ceramic titanate elements subsequently formed withthe powder.

After preparation of the desired barium titanate powder from said fourthsolution in the manner above described, the powder can be combined witha binder, dried, passed to form an intermediate element of selectedshape and is fired from forming ceramic titanate elements in the mannerpreviously described. As will be understood, semiconducting ceramictitanate materials can also be made with barium titanate powdersproduced from said fourth solution by adding a selected lanthanide saltor salts to the barium titanate in the manner previously described. Inaddition, such semiconducting ceramic titanate elements can also be madein a manner similar to that previously described wherein a lanthanidesalt is added to the fourth solution described above, the concentrationof said fourth solution being modified so that the molar quantity of theorganic titanium compound in the modified fourth solution substantiallyequals the sum of the molar quantities of alkaline earth and lanthanidesalts in the solution. For example, a barium lanthanum titanate materialhaving the empirical formula Ba La Ti O such as previously described canbe produced equally well beginning the process of this invention byproducing said fourth solution or a modification of said fourth solutionas it can by beginning the process of this invention with a combinationof the first and second solutions or with the third solution previouslydescribed.

It can be seen that the methods above described, reactant materials formaking ceramic-forming titanates are initially combined in a commonsolution so that the reactant materials are uniformily distributed withrespect to each other. Use of the titanium chelate of triethanolamine orthe tetraisopropyl titanate as the titanium-bearing reactant provides aninexpensive reactant material in highly purified form which is notsubject to crystalline transformation during processing as is thetitanium dioxide powder used in prior art processes. The rapid formationof a semisolid substance such as the noted gel or foam significantlyretards any tendency of the uniformily distributed raw materials tosegregate during reaction thereof so that, subsequent calcination andfiring of the reactant materials initially combined in the commonsolution provide ceramic materials of excellent homogeneity andconsistently reproducible physical and electrical characteristics in aprocess which is easily and inexpensively performed. The particle sizesin the ceramic titanate elements provided by this invention are alsosmall to assure relatively low voltage sensitivities when the elementsare used as solid-state sensors and the like.

It should be understood that although the methods of this invention havebeen described with reference to preferred embodiments of thisinvention, this invention includes all modifications and equivalents ofthe described methods which fall within the scope of the appendedclaims.

We claim:

1. A method for making a titanate material comprising the steps ofcombining an organic titanium material selected from the groupconsisting of titanium chelate of triethanolamine and tetraisopropyltitanate with at least one alkaline earth material in at least onesolvent, reacting said materials to form a semisolid substance, andheating said substance to form said titanate material.

2. A method for making a ceramic-forming titanate material comprisingthe steps of combining an organic titanium compound selected from thegroup consisting of tetraisopropyl titanate dissolved in an organic acidand titanium chelate of triethanolamine with at least one alkaline earthsalt in at least one solvent to form a common solution, heating saidcommon solution to fonn a semisolid substance, and calcining saidsubstance to form said ceramic-forming titanate material.

3. A method for making a titanate material comprising the steps ofdissolving titanium chelate of triethanolamine and at least one alkalineearth salt in at least one solvent to form a gel, and heating said gelto form said titanate material.

4. A method for making a ceramic-forming titanate material comprisingthe steps of dissolving titanium chelate of triethanolamine and at leastone alkaline earth salt in at least one solvent to form a commonsolution, heating said solution to form a gel, and calcining said gel toform said ceramicforming titanate material.

5. A method as set forth in claim 4 wherein said solution is heated at atemperature up to about 80 C. to form said gel, and wherein said gel isheated at a temperature between 600 C. and 1,150 C. for at least 1 hourfor calcining said gel to form said titanate material.

6. A method as set forth in claim 4 wherein said alkaline earth saltcomprises barium acetate.

7. A method for making a titanate material for use in formingsemiconducting ceramic elements comprising the steps of dissolvingtitanium chelate of triethanolamine, at least one alkaline earth salt,and at least one lanthanide salt in at least one solvent to form acommon solution, heating said solution to form a gel, and heating saidgel in an oxidizing atmosphere to form said titanate material.

8. A method for making a barium lanthanum titanate material ofperovskite structure having a curie point of approximately l25 C. foruse in forming semiconducting ceramic elements comprising the steps ofdissolving titanium chelate of triethanolamine, barium acetate, andlanthanum acetate in at least one solvent to form a common solution,heating said solution at a temperature up to about 80 C. to form a gel,and heating said gel in an oxidizing atmosphere at a temperature between600 C. and 1,150 C. to form said barium lanthanum titanate material.

9. A method for making semiconducting barium lanthanum titanate elementcomprising the steps as set forth in claim 8 and comprising theadditional steps of adding a binder to said barium lanthanum titanatematerial, pressing said material to form an intermediate element ofselected shape, and firing said intermediate element at a temperature ofat least l,300 C. to form said semiconducting barium lanthanum titanateelements.

10. A method for making a barium strontium lanthanum titanate materialhaving a curie point substantially lower than 125 C. for use in formingsemiconducting ceramic elements comprising the steps of combiningtitanium chelate of triethanolamine, barium acetate, strontium acetate,and lanthanum acetate in at least one solvent to form a common solution,heating said solution at a temperature up to about C. to form a gel, andheating said gel in an oxidizing atmosphere at a temperature between 600C. and l,l50 C. to form said barium strontium lanthanum titanatematerial.

11. A method for making semiconducting ceramic titanate elementscomprising the steps of dissolving titanium chelate of triethanolamineand at least one alkaline earth salt in at least one solvent to form acommon solution, heating said solution to form a gel, heating said gelin an oxidizing atmosphere to form a titanate material, combining saidtitanate material with an aqueous solution of a lanthanide salt and abinder material to form slurry, drying said slurry to form alanthanide-doped binder mixture, pressing said binder mixture to form anintermediate element of selected shape, and firing said intermediateelement at an elevated temperature to form said semiconducting ceramictitanate element.

12. A method as set forth in claim 11 wherein said alkaline earth saltcomprises barium acetate.

13. A method as set forth in claim 11 wherein said alkaline earth saltcomprises a mixture of barium acetate and strontium acetate.

14. A method as set forth in claim 11 wherein said lanthanide saltcomprises lanthanum acetate.

15. A method for making a titanate material comprising the steps ofdissolving tetraisopropyl titanate with an organic acid selected fromthe group consisting of acetic acid and watersoluble alphahydroxy acidsand with at least one alkaline earth salt in a solvent to form a commonsolution, and heating said solution to form a foamlike substance and tocalcine said substance to form said titanate material.

16. A method for making a ceramic-forming titanate material comprisingthe steps of dissolving tetraisopropyl titanate in a lactic acidsolution and adding at least one alkaline earth salt to said solution,heating said solution to form a foamlike substance, and calcining saidfoamlike substance to form said ceramic-forming titanate material.

17. A method as set forth in claim 16 wherein said solution is heated ata temperature between 600 C. and l,l50 C. for at least 1 hour forforming said foamlike substance and for calcining said foamlikesubstance to form said titanate material.

18. A method as set forth in claim 16 wherein said alkaline earth saltcomprises barium acetate.

19. A method for making a titanate material for use in formingsemiconducting ceramic elements comprising the steps of dissolvingtetraisopropyl titanate in an aqueous lactic acid solution and adding atleast one alkaline earth salt and at least one lanthanide salt in saidsolution to form a common solution, heating said common solution to forma foamlike substance, and heating said foamlike substance in anoxidizing atmosphere to form said titanate material.

20. A method for making a barium lanthanum titanate material ofperovskite structure having a curie point of approximately C. for use infonning semiconducting ceramic elements comprising the steps ofdissolving tetraisopropyl titanate in an aqueous lactic acid solutionand adding barium acetate and lanthanum acetate therein to form a commonsolution, heating said common solution at a temperature between 600 C.and l,l50 C. to form a foamlike substance and to calcine said substanceto form said barium lanthanum titanate material.

21. A method for making a semiconducting barium lanthanum titanateelement comprising the steps as set forth in claim and comprising theadditional steps of adding a binder to said barium lanthanum titanatematerial, pressing said material to form an intennediate element ofselected shape, and firing said intermediate element at a temperature ofat least l,300 C. to form said semiconducting barium lanthanum titanateelements.

22. A method for making a barium strontium lanthanum titanate materialhaving a curie point substantially lower than 125 C. for use in formingsemiconducting ceramic elements comprising the steps of combiningtetraisopropyl titanate dissolved in lactic acid with barium acetate,strontium acetate, and lanthanum acetate in at least one solvent to forma common solution, heating said solution at a temperature between 600 C.and l,i50 C. to form a foamlike substance and to calcine said substanceto form said barium strontium lanthanum titanate material.

23. A method for making semiconducting ceramic titanate elementscomprising the steps of dissolving tetraisopropyl titanate in an aqueoussolution of lactic acid, adding at least one alkaline earth salt to saidsolution, heating said solution in an oxidizing atmosphere to form afoamlike substance and to calcine said substance to form a titanatematerial, combining said titanate material with an aqueous solution of alanthanide salt and a binder material to form a slurry, drying saidslurry to form a lanthanide-doped binder mixture, pressing said bindermixture to form an intennediate element of selected shape, and firingsaid intermediate element at an elevated temperature to form saidsemiconducting ceramic titanate element.

24. A method as set forth in claim 23 wherein said alkaline earth saltcomprises barium acetate.

25. A method as set forth in claim 23 wherein said alkaline earth saltcomprises a mixture of barium acetate and strontium acetate.

26. A method as set forth in claim 23 wherein said lanthanide saltcomprises lanthanum acetate.

2. A method for making a ceramic-forming titanate material comprisingthe steps of combining an organic titanium compound selected from thegroup consisting of tetraisopropyl titanate dissolved in an organic acidand titanium chelate of triethanolamine with at least one alkaline earthsalt in at least one solvent to form a common solution, heating saidcommon solution to form a semisolid substance, and calcining saidsubstance to form said ceramic-forming titanate material.
 3. A methodfor making a titanate material comprising the steps of dissolvingtitanium chelate of triethanolamine and at least one alkaline earth saltin at least one solvent to form a gel, and heating said gel to form saidtitanate material.
 4. A method for making a ceramic-forming titanatematerial comprising the steps of dissolving titanium chelate oftriethanolamine and at least one alkaline earth salt in at least onesolvent to form a common solution, heating said solution to form a gel,and calcining said gel to form said ceramic-forming titanate material.5. A method as set forth in claim 4 wherein said solution is heated at atemperature up to about 80* C. to form said gel, and wherein said gel isheated at a temperature between 600* C. and 1,150* C. for at least 1hour for calcining said gel to form said titanate material.
 6. A methodas set forth in claim 4 wherein said alkaline earth salt comprisesbarium acetate.
 7. A method for making a titanate material for use informing semiconducting ceramic elements comprising the steps ofdissolving titanium chelate of triethanolamine, at least one alkalineearth salt, and at least one lanthanide salt in at least one solvent toform a common solution, heating said solution to form a gel, and heatingsaid gel in an oxidizing atmosphere to form said titanate material.
 8. Amethod for making a barium lanthanum titanate material of perovskitestructure having a curie point of approximately 125* C. for use informing semiconducting ceramic elements comprising the steps ofdissolving titanium chelate of triethanolamine, barium acetate, andlanthanum acetate in at least one solvent to form a common solution,heating said solution at a temperature up to about 80* C. to form a gel,and heating said gel in an oxidizing atmosphere at a temperature between600* C. and 1,150* C. to form said barium lanthanum titanate material.9. A method for making semiconducting barium lanthanum titanate elementcomprising the steps as set forth in claim 8 and comprising theadditional steps of adding a binder to said barium lanthanum titanatematerial, pressing said material to form an intermediate element ofselected shape, and firing said intermediate element at a temperature ofat least 1,300* C. to form said semiconducting barium lanthanum titanateelements.
 10. A method for making a barium strontium lanthanum titanatematerial having a curie point substantially lower than 125* C. for usein forming semiconducting ceramic elements comprising the steps ofcombining titanium chelate of triethanolamine, barium acetate, strontiumacetate, and lanthanum acetate in at least one solvent to form a commonsolution, heating said solution at a temperature up to about 80* C. toform a gel, and heating said gel in an oxidizing atmosphere at atemperature between 600* C. and 1,150* C. to form said barium strontiumlanthanum titanate material.
 11. A method for making semiconductingceramic titanate elements comprising the steps of dissolving titaniumchelate of triethanolamine and at least one alkaline earth salt in atleast one solvent to form a common solution, heating said solution toform a gel, heating said gel in an oxidizing atmosphere to form atitanate material, combining said titanate material with an aqueoussolution of a lanthanide salt and a binder material to form slurry,drying said slurry to form a lanthanide-doped binder mixture, pressingsaid binder mixture to form an intermediate element of selected shape,and firing said intermediate element at an elevated temperature to formsaid semiconducting ceramic titanate element.
 12. A method as set forthin claim 11 wherein said alkaline earth salt comprises barium acetate.13. A method as set forth in claim 11 wherein said alkaline earth saltcomprises a mixture of barium acetate and strontium acetate.
 14. Amethod as set forth in claim 11 wherein said lanthanide salt compriseslanthanum acetate.
 15. A method for making a titanate materialcomprising the steps of dissolving tetraisopropyl titanate with anorganic acid selected from the group consisting of acetic acid andwater-soluble alphahydroxy acids and with at least one alkaline earthsalt in a solvent to form a common solution, and heating said solutionto form a foamlike substance and to calcine said substance to form saidtitanate material.
 16. A method for making a ceramic-forming titanatematerial comprising the steps of dissolving tetraisopropyl titanate in alactic acid solution and adding at least one alkaline earth salt to saidsolution, heating said solution to form a foamlike substance, andcalcining said foamlike substance to form said ceramic-forming titanatematerial.
 17. A method as set forth in claim 16 wherein said solution isheated at a temperature between 600* C. and 1,150* C. for at least 1hour for forming said foamlike substance and for calcining said foamlikesubstance to form said titanate material.
 18. A method as set forth inclaim 16 wherein said alkaline earth salt comprises barium acetate. 19.A method for making a titanate material for use in formingsemiconducting ceramic elements comprising the steps of dissolvingtetraisopropyl titanate in an aqueous lactic acid solution and adding atleast one alkaline earth salt and at least one lanthanide salt in saidsolution to form a common solution, heating said common solution to forma foamlike substance, and heating said foamlike substance in anoxidizing atmosphere to form said titanate material.
 20. A method formaking a barium lanthanum titanate material of perovskite structurehaving a curie point of approximately 125* C. for use in formingsemiconducting ceramic elements comprising the steps of dissolvingtetraisopropyl titAnate in an aqueous lactic acid solution and addingbarium acetate and lanthanum acetate therein to form a common solution,heating said common solution at a temperature between 600* C. and 1,150*C. to form a foamlike substance and to calcine said substance to formsaid barium lanthanum titanate material.
 21. A method for making asemiconducting barium lanthanum titanate element comprising the steps asset forth in claim 20 and comprising the additional steps of adding abinder to said barium lanthanum titanate material, pressing saidmaterial to form an intermediate element of selected shape, and firingsaid intermediate element at a temperature of at least 1,300* C. to formsaid semiconducting barium lanthanum titanate elements.
 22. A method formaking a barium strontium lanthanum titanate material having a curiepoint substantially lower than 125* C. for use in forming semiconductingceramic elements comprising the steps of combining tetraisopropyltitanate dissolved in lactic acid with barium acetate, strontiumacetate, and lanthanum acetate in at least one solvent to form a commonsolution, heating said solution at a temperature between 600* C. and 1,150* C. to form a foamlike substance and to calcine said substance toform said barium strontium lanthanum titanate material.
 23. A method formaking semiconducting ceramic titanate elements comprising the steps ofdissolving tetraisopropyl titanate in an aqueous solution of lacticacid, adding at least one alkaline earth salt to said solution, heatingsaid solution in an oxidizing atmosphere to form a foamlike substanceand to calcine said substance to form a titanate material, combiningsaid titanate material with an aqueous solution of a lanthanide salt anda binder material to form a slurry, drying said slurry to form alanthanide-doped binder mixture, pressing said binder mixture to form anintermediate element of selected shape, and firing said intermediateelement at an elevated temperature to form said semiconducting ceramictitanate element.
 24. A method as set forth in claim 23 wherein saidalkaline earth salt comprises barium acetate.
 25. A method as set forthin claim 23 wherein said alkaline earth salt comprises a mixture ofbarium acetate and strontium acetate.
 26. A method as set forth in claim23 wherein said lanthanide salt comprises lanthanum acetate.